LM2675

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SNVS129E – MAY 2004 – REVISED JUNE 2005

TYPICAL SURFACE MOUNT PC BOARD LAYOUT, ADJUSTABLE OUTPUT (4X SIZE)

D1 - 1A, 40V Schottky Rectifier, Surface Mount

L1 - 68

μH, L30, Coilcraft DO3316

R1 - 1k, 1%

R2 - Use formula in Design Procedure

Figure 14. PC Board Layout

Layout is very important in switching regulator designs. Rapidly switching currents associated with wiring

inductance can generate voltage transients which can cause problems. For minimal inductance and ground

loops, the wires indicated by heavy lines (in Figure 7 and Figure 8) should be wide printed circuit traces

and should be kept as short as possible. For best results, external components should be located as close to

the switcher IC as possible using ground plane construction or single point grounding.

If open core inductors are used, special care must be taken as to the location and positioning of this type of

problems.

When using the adjustable version, special care must be taken as to the location of the feedback resistors and

the associated wiring. Physically locate both resistors near the IC, and route the wiring away from the inductor,

especially an open core type of inductor.

LLP PACKAGE DEVICES

The LM2675 is offered in the 16 lead LLP surface mount package to allow for increased power dissipation

compared to the SO-8 and DIP.

The Die Attach Pad (DAP) can and should be connected to PCB Ground plane/island. For CAD and assembly

guidelines refer to Application Note AN-1187 at http://power.national.com.

Copyright © 2004–2005, Texas Instruments Incorporated

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